Hi Everyone,
I pushed a major change to the pull request for the spec here:
https://github.com/Linaro/virtio-msg-spec/pull/16
I reworked the chapters and the content to look a lot more like other virtio transports and follow the sentence convention (MUST, SHALL, SHOULD).
Some sentences have been reworded with the help of chatgpt so we need to have a careful review of this but i think it looks a lot better than before.
please review based on the final content and not using the tree of patches as the last one is more or less rewriting everything.
Some things to think of:
- message format description: should we switch to structures instead of tables ? I did that for the header and channel I/O is using structures which might look better
- global terminology: i struggle a bit between driver/device vs frontend/backend and we must have a check on the coherency
- compliance: this is the bare output of chatgpt more for discussing than keeping it but it could give us ideas if we want to have something (Warning the compliance chapter content might be wrong).
As always: any comments are welcome :-)
Cheers
Bertrand
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Hi all,
I was wondering if the virtio-msg demos we have for FFA work on Xen?
I have some vague memory that they do.
I wonder if I can use the same lower-level virtio-msg-bus or ffa calls to move
messages between a DomU/Linux and a QEMU backend in Dom0?
Can someone point me to the code? Or documentation?
Thanks!
Best regards,
Edgar
Hi Everyone,
As you know we have a pending subject around Version handling to solve
to have some kind of "stable" version of the protocol and I think we have
a bit over engineered this so far so i will try to explain my current train of
thoughts so that we could have a productive discussion on Thursday.
What are other transports doing and why ?
- PCI: there is no real protocol version. Capabilities are used and there
is only one used for Legacy devices
- MMIO: One version register which an be 1 or 2, read only from the driver
which is used to inform a driver of the layout of the registers. There is no
negociation
- Channel I/O: A revision, a length and some way to set additional options
depending on the revision. The driver is here telling to the device which
revision of the protocol it wants to use and the device just say no if it
does not support what the driver wants. Once selected any change must be
rejected by the device and the driver must begin by setting it. Somehow
the virtio spec says that this is per device as the only change was a status
message not existing but it is clear that this must be handled at the transport
level and not in a specific driver.
What we need ?
I think we need something very close to what Channel I/O is defining and it
would be a good idea to do reuse the same principles:
- the driver side sets the revision
- the device side just say "Error" if it does not support what is requested
- once the revision is set, only a reset can allow to change it
- driver side should start with highest revision and go down until it finds
a revision it supports
Now I think that having this per device is not useful because we want to
have a generic transport and having different sets of messages per
device due to different revision seems like a complexity
we do not need.
So i think this is something that we should offload at the bus level and
define the following:
- A bus implementation must inform the virtio message generic
transport of the version of the protocol to be used for a specific bus
device instance (ie all devices on this instance will use the same
protocol version). This is to be done through an implementation
defined way.
- A bus implementation must inform the virtio message generic
transport of the maximum message size its support through an
implementation defined way. This can also be per bus device instance.
- It is the bus driver responsibility to negociate a version and maximum
message size with a bus device instance.
- It is the bus device responsibility to know which versions are supported
by its own virtio message generic implementation.
Follwing those principles i would propose to do the following changes in
the specification:
- remove the VIRTIO_MSG_VERSION message
- introduce a BUS_MSG_VERSION message with more or less the same
definition as the current VIRTIO_MSG_VERSION (only simplifying by
saying that the driver sets a version and device say yes or no, the size
would work as it is now)
Some questions for discussion:
- Do you think it is ok to move this to the BUS or should we keep it in
the generic layer to be more "coherent" with other transports ?
- Should we provision something like the "data" part in Channel I/O to
have options on a specific revision ?
- Anything else ?
Cheers
Bertrand
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.
Hi Everyone,
I pushed a new pull request to github on top of the current RFC status: https://github.com/Linaro/virtio-msg-spec/pull/13
This includes changes to handle some of the issues raised in github:
- have a version of the protocol
- have a variable message size
- have a configuration generation count
- give hint that bus implementation can be used for memory sharing or use of out of band notifications
Any comment is welcome :-)
Cheers
Bertrand
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All,
The RFC went out a bit ago.
I updated it based on Bertrand's and Arnaud's suggestions (cover letter,
commit description, and s/request/requests/ only).
(I also fixed a s/massage/message/ in the cover letter.)
Going forward the new baseline for spec work will be
virtio-msg-rfc1. This branch is now the default at the linaro repo [1].
Please target all new pull requests to this branch.
The virtio-msg-alpha branch is now frozen but will be kept for reference.
Thanks,
Bill
[1] https://github.com/Linaro/virtio-msg-spec
--
Bill Mills
Principal Technical Consultant, Linaro
+1-240-643-0836
TZ: US Eastern
Work Schedule: Tues/Wed/Thur
All,
I have updated the hvac-demo repo [1] with a new version.
This version is tagged: v0.5
The following outlines the changes since Jan 27:
* The demos can now be run on an arm64 host
(I tested with an AWS EC2 m7g.2xlarge instance)
(x86_64 testing was done on my desktop and AWS EC2 m7i.2xlarge instances)
* Pre-setup container images (amd64 & arm64) are published at
docker.io/wmills/havc-demo
* A convenience script ./container was added to make it easier to run a
container with a mounted directory
(This is an alternative to using the published container images and
suggested for building the demos)
* The ./container flow now requires the user to run ./setup themselves
(The pre-built container images already have ./setup done for both "run"
and "build")
* Fixes found from Dan's testing
* Building demo1
* Running demo3
* Running demo4
* Fixes found from Alex's testing (running on Debian-12 w/o container and
using tmux already)
* Handle tmux server already running
* Isolate from users .tmux.conf and default server
* (These fixes are not needed to run in a container)
* I have tested with podman and docker
* Most of my testing was done on clean EC2 machines w/ Ubuntu 24.04, both
x86_64 and arm64
* I also used my x86_64 desktop w/ Ubuntu 22.04
* I tested running the docker.io/wmills/hvac-demo images and the
./container flow
* Updated README.MD with simplified instructions including above
Thanks,
Bill
[1] https://github.com/wmamills/hvac-demo.git
--
Bill Mills
Principal Technical Consultant, Linaro
+1-240-643-0836
TZ: US Eastern
Work Schedule: Tues/Wed/Thur
Hi,
I just tried to run demo1 from a docker setup.
I can run the demo1 using docker but the demo does not work (some error 95 in kernel transmitting FF-A messages, it went out to far so i could not copy paste it).
Cheers
Bertrand
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.
This series adds the virtio-msg transport layer.
The individuals and organizations involved in this effort have had difficulty in
using the existing virtio-transports in various situations and desire to add one
more transport that performs its transport layer operations by sending and
receiving messages.
Implementations of virtio-msg will normally be done in multiple layers:
* common / device level
* bus level
The common / device level can be shared by all virtio-msg bus implementations
and defines the messages exchanged between the driver and a device. As with
other transport layers, virtio-msg should not require modifications to existing
virtio device implementations (virtio-net, virtio-blk etc). The common / device
level is the main focus of this version of the patch series.
The virtio-msg bus level implements the normal things a bus defines
(enumeration, dma operations, etc) but also implements the message send and
receive operations. A number of bus implementations are envisioned,
some of which will be reusable and general purpose. Other bus implementations
might be unique to a given situation, for example only used by a PCIe card
and its driver.
How much of the bus level should be described in the virtio spec is one item
we wish to discuss. This draft takes a middle approach by describing the bus
level and defining some standard bus level messages that MAY be used by the bus.
It also describes a range of bus messages that are implementation dependent.
The standard bus messages are an effort to avoid different bus implementations
doing the same thing in different ways for no good reason. However the
different environments will require different things. Instead of trying to
anticipate all needs and provide something very abstract, we think
implementation specific messages will be needed at the bus level. Over time,
if we see similar messages across multiple bus implementations, we will move to
standardize a bus level message for that.
We are working on two reusable bus implementations:
* virtio-msg-ffa based on Arm FF-A interface for use between:
* normal world and secure world
* host and VM or VM to VM
* Can be used w/ or with out a hypervisor
* Any Hypervisor that implements FF-A can be used
* virtio-msg-amp for use between heterogenous systems
* The main processors and its co-processors on an AMP SOC
* Two or more systems connected via PCIe
* Minimal requirements: bi-directional interrupts and
at least one shared memory area
We also anticipate a third:
* virtio-msg-xen specific to Xen
* Usable on any Xen system (including x86 where FF-A does not exist)
* Using Xen events and page grants
This series is a work in progress and we acknowledge at least the following
issues we need to work on:
* Conform to virtio spec nouns (device/driver vs frontend/backend)
and verbs (must/may)
* Perhaps move error definition elsewhere it the spec and align on its symbols
and numeric values
* Allow massage size to be greater than 40 bytes and allow bus implementations
to define their max message size
* Add a way to discover the protocol version
* Add a better description of the types of things a bus can do, specifically
including out-of-band notification and memory area sharing/discovery
* Maybe redo configuration generation handling
Background info and work in progress implementations:
* HVAC project page with intro slides [1]
* HVAC demo repo w/ instructions in README.md [2]
* Kernel w/ virtio-msg common level and ffa support [3]
* QEMU w/ support for one form of virtio-msg-amp [4]
* Portable RTOS library w/ one form of virtio-msg-amp [5]
In addition to the QEMU system based demos in the hvac-demo repo, we also have
two hardware systems running:
* AMD x86 + AMD Arm Versal connected via PCIe
* ST STM32MP157 A7 Linux using virtio-i2c provided by M4 Zephyr
Please note that although the demos work, they are not yet aligned with each
other nor this version of the spec.
[1] https://linaro.atlassian.net/wiki/spaces/HVAC/overview
[2] https://github.com/wmamills/hvac-demo
[3] https://git.kernel.org/pub/scm/linux/kernel/git/vireshk/linux.git/log/?h=vi…
[4] https://github.com/edgarigl/qemu/commits/edgar/virtio-msg-new
[5] https://github.com/arnopo/open-amp/commits/virtio-msg/
Bill Mills (1):
virtio-msg: Add virtio-msg, a message based virtio transport layer
content.tex | 1 +
transport-msg.tex | 680 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 681 insertions(+)
create mode 100644 transport-msg.tex
--
2.34.1
Hi Viresh,
I'll try to respond to your first question: indirect messages require FF-A
notifications, and Trusty does not support those either.
The problem isn't Trusty specifically, but the layers between it and Linux:
the hypervisor and SPMC.
To be as specific as I can: Hafnium supports notifications, but others
don't.
For now, we'll need to work around this in virtio-msg-ffa with direct
messages and polling.
Andrei Homescu
Hi Ayrton / Armelle,
I tried to investigate about how to make VIRTIO_MSG_EVENT_USED work without
indirect FFA messages.
- Firstly, I am still not sure if I fully understand why indirect messages can't
be implemented on Trustee side ? I know it was discussed a bit in the call,
but I don't remember any of it :(
- If we want to do polling of the virtqueues, then it needs to be done on the
driver side (vsock), I don't see how I can generalize it and do it from
virtio-msg-ffa layer. The driver needs to do something like this for the
virtqueue:
while (1) {
/* Try to get a buffer from the virtqueue */
buf = virtqueue_get_buf(vq, &len);
if (buf) {
// Handle the received buffer
break;
}
/* Avoid busy looping with a small delay */
cpu_relax();
}
- The other idea discussed on the call was about always queuing a direct message
for a FFA device (not virtio device) for EVENT_USED message. Once the trustee
side has an event to send, it can respond to this request.
I was thinking if this may block the CPU for ever with the SMC call, but I
don't think that is the case. The FFA layer makes the SMC call, checks its
return value and sleeps for a ms, and tries again. With this the CPU will
schedule other work as soon as it can. And looks like we support sending
multiple direct messages concurrently too, so while a thread is waiting for a
response to EVENT_USED message, we can keep sending other messages.
If we want to support this, will this be part of the spec ? Bertrand ?
- Any other ideas on how to get this solved ?
--
viresh
